It is known to construct a disk drive by rotationally mounting a disk assembly to a base via conductive metal ball bearings. In such a case, the electrical grounding path provided through the metal ball bearings tends to prevent static electric build up on the disk assembly, thereby preventing harmful discharges through the read/write head.
It is also known to use ceramic ball bearings in place of metal ball bearings to reduce disk run-out. In this case, an electrically conductive grease may be used in the bearing in order to ground the disk assembly, as disclosed in U.S. Pat. No. 6,250,808. However, the quality of the grease may deteriorate over time, leading to breakdown of the ground path and potentially allowing harmful electrostatic discharge to occur.
Another known grounding technique employs one or more cantilever wipers that are pressed against the rotating spindle of the disk assembly, as disclosed in U.S. Pat. No. 5,251,081. However, the contact between parts in relative motion to each other may generate particles, and the ground path may have a limited life due to wear.
According to other proposals, as disclosed in U.S. Pat. Nos. 5,761,009 and 6,259,573, an alternative discharge path is provided through the actuator arm to prevent an electrostatic discharge from passing through the magneto-resistive sensor. Although such arrangements may prevent damage to the read-write head, there still remains the possibility of damage to the data storage disk surface.
Still another arrangement that could be contemplated for preventing harmful electrostatic discharges in a disk drive might entail injecting ionized air into the drive, as is done in testing equipment such as flying height testers (see U.S. Pat. No. 5,696,585). However, cost and space constraints make injection of ionized air impractical for commercial disk drives.
In view of the foregoing, it would be desirable to provide an improved technique for preventing harmful electrostatic discharges in disk drives. Another reason for preventing voltage buildup on data storage disks is that increased voltage may attract particles that may contaminate the disk surface, possibly leading to a head crash. The problem of electrostatic buildup can be particularly acute for disk drives that are operated at high temperatures, since in such a case the ambient air becomes very dry.